Heat recovery process in coal gasification

ABSTRACT

An overall process of cooling, dust removal, tar removal and heat recovery of high temperature gas generated in coal gasification furnaces, and apparatuses employed therefor are provided. In this process, specific apparatuses such as fluidized bed-cooler, fluidized bed-combustion furnace for regenerating granules, granular bed filter, gas cooler, and tar scrubber are successively and effectively employed. During the process, high, medium and low pressure steam, for example, are recovered by heat exchange in these apparatuses.

This is a division of application Ser. No. 228,775, filed Jan. 27, 1981,now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an overall process of cooling, dust removal,tar removal and waste heat recovery of high temperature gas generated incoal gasification furnaces, and also to apparatuses employed in theabove process.

2. Description of the Prior Art

According to one of processes for coal gasification, coal is gasified byreacting it with hydrogen, steam or the like at high temperatures andhigh pressures. Such gases generated from coal gasification furnaceshave high temperatures of 800° to 1000° C. and contain dust such asundecomposed coal, ash, etc., byproduced tar, pitch, oil mist, etc.;hence in order to effectively utilize such gases, gas cooling, dustremoval and tar removal are necessary, and at the time of cooling, it isalso necessary to recover the waste heat by effective means.

The gas cooling has heretofore included two manners: usual tubular heatexchange and direct spouting of cooling medium. However, the tubularheat exchange employing shell-and-tube heat exchangers has drawbacks inthat the tar contained in the cooled gas adheres onto the surface ofheat transfer tubes, etc. and solidifies there to inhibit not only theheat transfer performance of the tubes, but also the gas flow functionthereof. On the other hand, the latter cooling manner of directlyspouting a lower temperature oil or the like into the gas is alsouneconomical, since the sensible heat of the gas is scatteredwastefully.

SUMMARY OF THE INVENTION

An object of this invention is to provide a process for removing dustfrom the high temperature gas generated from the plants for coalgasification and also cooling the gas without any adhesion andsolidification of tar and the like.

Another object of this invention is to provide a process for effectivelyrecovering the sensible heat of the high temperature gas and also fullyrecovering the heat generated from the additional treatment of the gasin the coal gasification process.

A further object of this invention is to provide apparatuses suitablyemployed for dust removal from, cooling of and heat recovery from thehigh temperature gas.

A still further object of this invention is to provide a heat-exchangemeans capable of establishing such a safe temperature that tar containedin the gas does not solidify even when it is condensed; a heat-exchangemeans having a structure capable of discharging the condensed tar byflow-down and maintaining the surface of heat transfer tubes in itsnormal state; and further a cooler capable of improving the gas coolingefficiency and also removing dust from the gas by direct contact of oilwith the gas and cooling of the gas thereby.

According to the present invention, a process is provided which mainlycomprises passing the gas generated in coal gasification furnacesthrough a fluidized bed-cooler provided therein with heat transfer tubeshaving cooling medium such as water passed therethrough, to thereby coolthe generated gas and recover the heat of the gas in the form of hotwater or steam, for example, and at the same time remove unnecessarysubstances contained in the gas through adhesion thereof onto thefluidizing medium constituting the fluidized bed.

In the above process, it is preferable to exchange heat between chardischarged from the coal gasification furnaces and cooling medium torecover the heat of the char in the form of hot water or steam, forexample, and combine this hot water or steam with that obtained in theabove fluidized bed-cooler.

As the fluidized bed-cooler employed in the present invention, anapparatus is preferable which comprises a body consisting of avertical-type vessel; a downcomer through which cooling medium ispassed, passing through the axially central part of the fluidized bed ofa fluidizing medium to be formed inside the body; a manifold provided atthe lower end part of the downcomer; a group of heat transfer tubesextending radially from the manifold and then extending upwards inparallel to the flow of gas to be sent from the lower part of the body;and a header connected to the upper ends of the heat transfer tubes.

In the above process of the present invention, the fluidizing mediumcontained in the fluidized bed-cooler, onto which unnecessary substancescontained in the gas have adhered are preferably treated such that thefluidizing medium is withdrawn from the fluidized bed-cooler andsubjected to combustion treatment in a fluidized bed-combustion furnaceto regenerate the fluidizing medium, and at the same time the heatgenerated by the combustion treatment is recovered by heat exchange withcooling medium contained in heat transfer tubes provided in thefluidized bed-combustion furnace.

Further, according to the present invention, an overall process forcooling, dust removal from the heat recovery from the gas generated incoal gasification furnaces is provided which comprises; a step ofintroducing the gas into a granular bed means such as a fluidized bedcooler and/or a moving bed filter, cooling the gas by cooling mediumpassed through heat transfer tubes provided inside said granular meansand at the same time recovering heat from the generated gas by heatexchange with the cooling medium; and a step of passing the gas cooledin said granular bed means, successively through a gas cooler and ascrubber, to cool the gas and remove dust and tarmist therefrom, andthrough the cooling and scrubbing of the gas in said gas cooler and saidscrubber, recovering waste heat from the gas.

As the cooling medium, materials having gas-liquid phase change at anappropriate temperature, such as water, alcohols, and other organic andinorganic ones can be employed.

In the case of employing water as the cooling medium, a typical processaccording to the present invention comprises the following steps; a stepof introducing the generated gas into a fluidized bed-cooler, coolingthe gas by cooling water passed through heat transfer tubes providedinside the fluidized bed-cooler and at the same time recovering the heatof the generated gas in the form of high pressure steam; and a step ofpassing the gas cooled in the fluidized bed-cooler, successively througha granular bed filter, a gas cooler and a scrubber wherein oil,preferably a recovered tar is sprayed to cool the gas and remove dustand tar mist therefrom, and during the cooling of the gas in said gascooler and said scrubber, generating medium pressure steam in the gascooler and low pressure steam in the scrubber, respectively, for wasteheat to be recovered.

As the granular bed filter employed in the above process, an apparatusis preferable which comprises a body consisting of a vertical typevessel; a gas-introducing passage provided at the axially central partof the body; a plurality of louver-form walls provided so as toconcentrically surround the gas-introducing passage; a means for formingmoving beds by feeding medium of granules in the respective ring-formspaces between these louver-form walls; and nozzles for discharging thegas having passed through the louver-form walls and the moving beds ofgranules to the outside of the body, the respective upper ends of thelouver-form walls being fixed onto the body by a granule-feeding duct,the respective lower ends of the louver-form walls being connected to agranule-discharging duct, and the respective granule-discharging ductbeing slidably contacted with the opening part of the body at the endpart thereof so as to allow these granule-discharging ducts to expandthermally.

The regenerated granules obtained by feeding granules having substancesadhered thereonto to a regeneration furnace consisting of a fluidizedbed-combustion furnace and subjecting the granules to combustiontreatment therein, are preferably recirculated to the granular bedfilter and/or the above-mentioned granular bed-cooler.

As such a fluidized bed-combustion furnace, an apparatus is preferablyemployed which comprises a body of a vertical type vessel, upper andlower stage fluidized beds contained therein, which are connectedthrough a vertical overflow pipe. In the upper stage fluidized bed,combustible substances adhering to the granules are burnt, and in thelower stage fluidized bed, air to be fed to the upper stage fluidizedbed is preheated and at the same time the regenerated granules flowingdown through the overflow pipe are cooled.

For cooling the gas having left the granular bed filter and alsoremoving tar mist therefrom, the above-mentioned gas cooler ispreferably of a vertical type wherein a plurality of heat transfer tubesthrough which cooling water is passed are vertically arranged. Theabove-mentioned scrubber is preferably a vessel wherein the lower endsof the above-mentioned heat transfer tubes are opened and nozzles forspraying recovered tar into the vessel are provided. The gas cooled bypassing through the heat transfer tubes is introduced directly into thescrubber where the gas is contacted with recovered tar, and tar mist inthe gas is removed. It is preferable to maintain the wall temperature ofthe heat transfer tubes at 200° C. or higher to avoid adhesion andsolidification of tar.

The above-mentioned gas cooler is connected to a condensation drumthrough a riser and a downcomer, and the heat of the gas passing throughthe heat transfer tubes inside the gas cooler is recovered in the formof such medium pressure steam as 15 kg/cm² G, through the condensationdrum and heat transfer tubes inside the drum.

Further, the scrubber is further connected to a gas-liquid separatorsuch as cyclone and is provided with a means for recirculating the tarcondensed in the gas-liquid seaprator to the scrubber and also a heatexchange means for recovering the heat of the recovered tar in the formof low pressure steam of 3 kg/cm² G.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a flow diagram illustrating a process of cooling, dustremoval, tar removal and heat recovery of the gas generated in coalgasification furnaces, in which process a fluidized bed-cooler isemployed.

FIG. 2 shows a cross-sectional view of an embodiment of the fluidizedbed-cooler employed in the present invention.

FIG. 3 shows a cross-sectional view of the fluidized bed-cooler cutalong III--III line of FIG. 2 in the direction of arrow marks.

FIG. 4 shows a block diagram illustrating a preferable embodiment of anoverall process according to the present invention, for cooling, dustremoval, tar removal, and heat recovery of the gas generated in coalgasification furnaces.

FIG. 5 shows a flow diagram including a combination of concreteapparatuses to be employed in the overall process shown in FIG. 4.

FIG. 6 shows a cross-sectional view of the granular bed filter shown inFIG. 5.

FIG. 7 shows a cross-sectional view of the granular bed filter cut alongVII--VII line of FIG. 6 in the direction of arrow marks.

FIG. 8 shows a flow sheet including a combination of apparatuses forregenerating the medium granules contained in the granular bed filter,in an atmosphere of normal pressures and recirculating the regeneratedgranules to the granular bed filter.

FIG. 9 shows a cross-sectional view of the fluidized bed-combustionfurnace for regenerating the medium granules from the granular bedfilter.

FIG. 10 shows a flow diagram illustrating a gas cooler and a scrubberfor further cooling the gas discharged from the granular bed filter andremoving tar mist therefrom,

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a process for cooling, dust removal, tar removal andwaste-heat recovery of coal gas, employing a fluidized bed-cooler isillustrated in FIG. 1.

Coal inside a hopper 2 is fed to a reaction zone 5 inside a coalgasification furnace 1 where a gasification reaction is carried out at ahigh temperature and a high pressure together with a gasifying agent 3such as hydrogen, steam (H₂ O), etc. introduced therein. The gasgenerated by this reaction is led from the top of the furnace 1 into adust collector 7 such as cyclone where dust contained in the gas isremoved, and the collected dust is returned to the furnace 1. Residualchar (abbreviated hereinafter to "Char") formed by the gasificationreaction is discharged from the lower part of the furnace and flows intoa char cooler 6 where heat exchange is carried out between the char andcooling water W fed through a piping 15A from a drum 13 to recover theheat of the char while the char being cooled. On the other hand, thereaction gas having left the dust collector 7 is led into a fluidizedbed-cooler 9 wherein heat transfer tubes 14 are provided and afluidizing medium such as sand is fluidized by introducing the reactiongas to form a fluidized bed 20. Cooling water W is flown from the drum13 via a piping 15B into the heat transfer tube 14 inside the fluidizedbed 20 to effect heat exchange between the cooling water and thereaction gas, resulting in the gas being cooled. At that time, tar,pitch, oil mist, etc. contained in the reaction gas adhere onto thesurface of the fluidizing medium constituting the fluidized bed, whichresults in removal of unnecessary components contained in the reactiongas. After completion of the cooling and the removal of unnecessarycomponents, the reaction gas enters a dust collector 12 where dust isremoved, and then discharged to the outside of the system. On the otherhand, a part of the fluidizing medium inside the fluidized bed-cooler 9,having unnecessary components adhered thereonto, is extracted at thelower part of the cooler to the outside and led into a hopper 11 for theextracted medium. The medium inside the hopper 11 is fed through ametering feeder 21 such as rotary feeder into a regeneration furnace 22wherein organic components such as tar adhering to the medium are burnt.This regeneration furnace 22 is a fluidized bed furnace wherein afluidized bed is formed by the medium extracted from the cooler 9 andfluidizing air A, and the components adhering onto the surface of thefluidizing medium are burnt. At that time, as in the cases of the charcooler 6 and the cooler 9, cooling water W inside the drum 13 is fed viaa piping 15C into a heat transfer tube 23 inside the fluidized bed forheat recovery. After completion of the regeneration by burning, thefluidizing medium is transferred to a hopper 10 for the fluidizingmedium and then fed via a valve 25 into the fluidized bed-cooler 9.

In the above-mentioned process, the respective portions of cooling waterW, after having effected heat exchange in the char cooler 6, thefluidized bed-cooler 9 and the regeneration furnace 22, are returned viapiping 24A, 24B and 24C to the drum 13, in the form of hot water orsteam, and a portion of the steam is then discharged via a piping 17 tothe outside of the system for utilization. Numeral 16 shows a pipe forfeeding water W to the drum 13.

A representative embodiment of the fluidized bed-cooler 9 employed inthe above-mentioned process is shown in FIG. 2 and FIG. 3.

In FIG. 2, the body of the fluidized bed-cooler 26 is verticallycylindrical and its lower part constitutes a conical spouting part 28, afluidizing medium being filled inside this spouting part 28 and acylindrical part connected thereto. Further, inside the body of thecooler 26 is provided a downcomer 30 extending downwards through thecentral part of the fluidized bed toward the spouting part 28, the lowerend of which downcomer 30 constitutes a manifold 32. Between thismanifold 32 and a ring-form header 34 provided on the inner wall of thebody of the cooler at the upper part of the fluidized bed, are placed aplurality of heat transfer tubes 36 which are each radially extended outfrom the manifold 32 toward the inner wall of the body of the coolingapparatus 26, then bent upwards by about 90° to the radially extendedpart 36A and constitute a main heat transfer part 36B arranged inparallel to the direction of the reaction gas flow, and finallyconnected to the header 34 arranged in ring form relative to the innerwall of the body.

Reaction gas 38 at a high temperature flows into the body 26 through anozzle 40 provided at the spouting part 28, and fluidizes the fluidizingmedium during its ascending inside the body 26, to form a fluidized bed20. The high temperature gas 38 transfers its heat to the fluidizingmedium and heat transfer tubes and is cooled during its passage throughthe fluidized bed 20, while the components contained in the reactiongas, i.e. tar, pitch, oil mist, etc. adhere to the fluidizing medium andare removed from the gas. Next, the fluidizing medium having atemperature elevated by the heat exchange between the medium and thereaction gas and having the components adhered thereto, is withdrawnfrom the body through a nozzle 44, while a fresh fluidizing medium isfed through a nozzle 46 to thereby keep the height of the fluidized bedat a definite one.

On the other hand, the heat transfer medium 48 (cooling medium) such aswater passes through the downcomer 30 which descends through the centralpart of the fluidized bed 20 toward the spouting part 28, to themanifold 32 as a distributor, where the medium reverses its directionand ascends through heat transfer tubes 36. Thus, the heat transfermedium 48 inside the heat transfer tubes effects heat exchange betweenthe medium and the reaction gas to cool the gas, while the medium itselfis heated and discharged to the outside of the system in the form of hotwater or steam (in the case where the heat transfer medium is water).After completion of the heat exchange, the reaction gas is led throughthe fluidized bed 20 to an empty column part 42. Since this empty columnpart 42 has a larger cross-sectional area than that of the cylindricalpart located therebelow, the gas flow rate is reduced to cause thefluidizing medium whirled up by the gas flow to fall down, while the gasis discharged from an exit nozzle 50.

In the above-mentioned cooling process, the inside temperature of thefluidized bed is detected by a temperature of the empty column part, bya temperature detector 54, to adjust the amounts of the fluidizingmedium fed and discharged and the amount of the heat transfer mediumintroduced, and also control the extent to which the reaction gas iscooled. In addition, numeral 56 shows a nozzle employed for discharginga large amount of the fluidizing medium. Numeral 58 shows a rotaryvalve.

Since the heat transfer pipes arranged inside the fluidized bed arelocated in parallel to the flow direction of the reaction gas, thefluidized bed-cooler 9 does not hinder the fluidization of thefluidizing medium; hence it is possible to effectively carry out thecooling of the reaction gas and the heat recovery therefrom.

Next, a block diagram of the overall process for carrying out cooling,dust removal, tar removal and heat recovery of the gas generated in coalgasification furnaces is shown in FIG. 4, and a concrete embodimenttherefor is shown in FIG. 5.

In this overall process, as is shown in FIG. 4, the gas generated in thecoal gasification furnace 1 is passed through a fluidized bed-cooler 9,a granular bed filter 60, a gas cooler 62 and a scrubber 64 to carry outdust removal and gas cooling, while three kinds of high pressure steam(HPS), medium pressure steam (MPS) and low pressure steam (LPS) aregenerated to effect waste heat recovery.

The gas generated in the coal gasification furnace 1 contains e.g.several grams of dust per Nm³, and also tar in an amount of at the mostabout 3%, based on the amount of coal treated is byproduced and presentin the form of mist in the high temperature gas. In FIG. 5, the coal gasis first subjected to rough removal of dust in a cyclone 7 and then sentthrough a duct 66 to the fluidized bed-cooler 9 in the form of a gas ofa high dust content such as several grams per Nm³. The fluidizedbed-cooler 9 is constituted by a heat transfer tube 14 provided insidethe fluidized bed 20 in the body of the cooler, a boiler drum 68, ariser 70 and a downcomer 72, and granules as the fluidizing medium suchas alumina granules of 1 to 2 mm in diameter are fluidized by theabove-mentioned gas inside the body of the cooler to form a fluidizedbed 20. The sensible heat of the gas is transferred by the medium of thegranules to the heat transfer tube 14 to generate steam. The gas iscooled down to a temperature level e.g. 400° to 500° C. at which thefluidization is maintained, in the cooler 9, without any sticking of thegranules with each other and any solidification thereof in the fluidizedbed. Thus, the pressure of the steam to be recovered, inside the heattransfer tube 14 is also sufficiently elevated up to a pressurecorresponding to the above temperature, e.g. 60 to 100 kg/cm² G, wherebythe temperature of the heat transfer surface is maintained. Bymaintaining the temperature of the heat transfer surface at 400° to 500°C. as described above, it is possible to clean the dirty heat transfersurface through the contacting and self-cleaning action of the granules.In addition, numerals 67 and 69 show a water-feeding pipe to and asteam-discharging pipe from the boiler drum 68, respectively.

Since a small amount of tar adheres onto the surface of the granulesinside the fluidized bed-cooler 9, the granules are quantitativelywithdrawn through an overflow pipe 74, and further sent via a rotaryvalve 76 to a regeneration furnace 22, where the granules are subjectedto regeneration treatment. On the other hand, the gas having left thefluidized bed-cooler 9 is sent via a duct 78 to a granular bed filter 60wherein granules of e.g. alumina 82 similar to those employed in thecooler 9 are filled. The granules are quantitatively withdrawn through apipe 84 and a rotary valve 86 while forming a moving bed in the filter60. The dust-containing gas leaves the dust in the granular bed when itis passed through the bed, and the resulting cleaned gas is dischargedthrough a duct 88. For the dust removal at high temperatures, thegranular bed is most suitable, since conventional mechanicaldust-collectors such as cyclone have a drawback in that adhesion of dustonto the wall of the collectors, occurs and causes clogging etc., whileelectric precipitators have a temperature limitation beside the dustadhesion. In addition, although it is functionally possible to removedust from the gas having a high temperature close to 1000° C. at theexit of the coal gasification furnace, by means of the granular bed, itencounters a structural difficulty to make the mechanical elements forwithdrawing and feeding the granules, resistant to such a hightemperature. Thus, when a fluidized bed-cooler as a means for coolingthe high temperature gas containing dust and tar is used whilerecovering heat from the gas, a combination of such a fluidizedbed-cooler with the granular bed is very effective.

As to the granules 82 in the granular bed, those of the samespecification as in the fluidized bed-cooler may be convenientlyemployed. The granules withdrawn from the granular bed 60 are thentreated in the regeneration furnace 22 which is a fluidizedbed-combustion furnace and in which the granules are fluidized bycombustion air 92 and dust and substances adhering onto the surface ofthe granules are subjected to combustion treatment by the aid of acombustion-aiding oil. Numeral 91 shows the granular fluidized bed.Numeral 93 and 95 each show a heat transfer tube provided inside thefluidized bed and at the top of the column, respectively. Numeral 97shows a gas-discharging pipe.

The granules thus regenerated are withdrawn from the regenerationfurnace 22 through an overflow pipe 94, and then transferred bycompressed air fed through a pipeline 99, by means of a blowing-up means96 through a pipe 98 to a hopper 100. The compressed air is separatedfrom the granules and exhausted from a pipeline 102. The regeneratedgranules are fed through rotary valves 103 and 104, feed pipes 105 and106 again to the fluidized bed-cooler 9 and the granular bed 60.

The gas free of dust is further cooled by the cooler 62 and led througha short pipe 110 to the scrubber 64. The cooler 62 has a heat transferpipe 113 through which cooling water is passed, which is connected to aboiler drum 109 via a riser pipe 111 and a downcomer 112. Feed water 114to the boiler drum 109 is introduced into the drum 109, vaporized andwithdrawn therefrom in the form of medium pressure steam 115. The tarcontained in the gas has a limitation to fluidity in the vicinity of150° C.; hence unless the inside of the cooler 62 is maintained abovethe temperature of 150° C., adhesion and solidification of tar occur.Thus, heat recovery in the cooler 62 is made so as to give steam whosesaturation temperature corresponds to 200° to 250° C. As one of examplesdesigned, a medium pressure steam of 15 kg/cm² G at a gas temperatureafter cooling, of 250° C. and a wall temperature of the heat transfertube above 200° C. may be employed.

In the scrubber 64, recovered tar is spouted directly into the scrubberto further cool the gas and at the same time remove the tar contained inthe gas.

Even if the bed of the granular bed filter 60 is provided in a pluralityof stages, the efficiency of dust removal has a limitation, but in thecase where the scrubber 64 is further provided as mentioned above, asufficient dust removal can be effected.

The gas having left the scrubber 64 is sent through a duct 108 to agas-liquid separator such as cyclone 116 where gas-liquid separation iscarried out, and then sent through a pipeline 118 to the outside of thesystem, while recovered tar is sent through a piping 120 to a tar pot122.

The tar temperature in the tar pot 122 is in the vicinity of 200° C.that is the same temperature as that of a separated gas 118; hence thetar is further cooled in a waste heat boiler 126 in order to elevate thecooling performance of the tar in the scrubber 64. Namely, there isformed a circulation line of recovered tar consisting of an exit piping124 from the tar pot 122, a pump 125, a boiler 126 and a piping 127, tocarry out cooling of the tar and at the same time heat recovery. Excesstar is discharged through a piping 128 and utilized as thecombustion-aiding oil for the regeneration furnace 22. As a designexample of the boiler 126, a boiler inlet temperature of 250° C. and anexit temperature of 150° C. are illustrated, and steam 131 generated ina drum 130 is of a low pressure of about 3 kg/cm² G. Numeral 132 showsfeed water to the drum 130. In addition, if the waste heat boiler 126 isreplaced by a water cooler, the heat transfer pipe is ruled by watertemperature; hence the tar temperature becomes lower, resulting in tarsolidification. Thus, it is most preferable to employ a low pressureboiler here.

A preferable embodiment of the granular bed filter 60 shown in FIG. 5 isillustrated in FIG. 6. FIG. 7 shows a cross-sectional view of the filtercut along the line VII--VII of FIG. 6 in the arrow direction.

In general, such a dust-removing means of the granular bed type iseffective for treating gases at high temperatures and high pressures.According to such a means, when a dust-containing gas is passed througha moving bed of slowly moving granules (abbreviated hereinafter to"bed"), the dust is caught by the granules, separated from the gas, andwithdrawn from the bed along with the granules. Although there is theso-called kiesbed means employing fine particles such as sand, thegranular bed means generally refers to the one employing granulated,calcined granules of e.g. alumina having a granular diameter of 1 to 2mm. As to the efficiency of dust removal, for example in case where thedust removal is applied to a process for low calory gasification of coalby a partial oxidation with air, experimental results show that when thethickness of the bed through which the gas passes is in the range of 300to 600 mm, the efficiency of dust removal at one stage (one layer) is inthe vicinity of 90%, whatever moving rate of alumina granules may beemployed. Thus, in order to sufficiently elevate the efficiency of dustremoval up to 95% or higher, it is required to employ a plurality ofstages as the bed. Further, the granules should be moved at a definiterate by metering charge and discharge between partition walls. In thecase of high temperature gas, a countermeasure to absorption of thethermal expansion of members constituting these partition walls isrequired, and moreover, it is also required to pay attention so that thegas may not be shorted.

The granular bed filter shown in FIG. 6 is constructed as follows: atthe axially central part of a vessel is located a gas-introducingpassage around which a plurality of layers of louver-form walls areprovided, and a large number of granules such as small sphericalmaterials are fed in the spaces formed between the respective walls toform moving beds to thereby enable the gas to pass through the surfacesof the walls and the moving beds; one or more nozzles for dischargingthe gas are provided through the wall of the vessel; and the lower endparts of the louver-form walls are constructed so as to give an easilyheat-expansible, thermal sleeve structure, without constraining eachother.

The body of the bed 134 is a heat-resistant, pressure vessel having atop part end-plate 135 and a bottom part end-plate 136 connected by abody flange 137, its inner surface being lined by a heat insulationmaterial. The body 134 has support-lugs 139 fixed thereto and verticallyarranged on a pedestal. The dust-containing gas enters the body 134through an upper part nozzle 140, passes through a cone duct 141 whereinthe flow rate of the gas is reduced, and enters a cylindrical gaschamber 142 located at the central part of the vessel. The lower part ofthe gas chamber 142 is partitioned by a plate 143. Thus, the gas is ledthrough a first stage louver 144 on the lateral side of the chamber,into a ring-form first stage bed 145 concentric with the gas chamber.The partitioning plate 143 is shaped into a mountain form protrudedupward as shown in FIG. 6. This aims at preventing tar, oily materials,etc. from deposition and permitting the gas to be uniformly distributedin the louver at the lower part of the vessel.

Adjacently to the first stage bed, a ring-form intermediate gas chamber147 and then a ring-form second stage bed 146 are located concentricallywith the first stage bed. The gas is led from the gas chamber 142located at the central part, through the louver 144 and then the firststage bed 145 into the intermediate gas chamber 147, and further througha louver 148 and then the second stage bed 146, and gathered in an outerperipheral space 149. The concentric conditions of the above-mentionedfirst stage bed 145, intermediate gas chamber 147, second stage bed 146and outer peripheral space 149 will be more easily understood byreferring to FIG. 7. In short, while the gas is passed through the firststage bed 145, the intermediate gas chamber 147 and the second stage bed146, radially from the central part of the body of the vessel 134 towardits outer periphery, dust is caught between the granules contained inthe two beds 145 and 146 to give dust-free gas, which is then passedthrough an outer peripheral gas chamber 149; gathered in a gas passage151 formed by a partitioning plate 150 inside the top part end-plate;and discharged through one or more discharge nozzles 152. The granulesin the first stage bed 145 are fed in metering manner through a nozzle153, fall through a cone 154 and enter a space formed between thelouvers 144, in which the first stage bed is formed.

The bed 145 placed between the concentric, ring-form louvers 144 has abed thickness of e.g. 500 to 600 mm in which the granules are filled,and the end part of the outer louver 144 is connected to a downcomer 157through a cone 156, which downcomer 157 is fit in a sleeve 158 connectedto an exit nozzle 159, in a loose contact manner, to form the so-calledthermal sleeve. The taper angle of the cone 156 is made sufficientlysmaller than the angle of repose of the granules so that the granulesmay fall easily. By constructing the first stage bed 145 as describedabove, it is possible to easily pass the gas through the bed 145 andalso to permit the granules to fall smoothly without their springing outof the bed.

The second stage bed 146 is similar to the first one in the constructionexcept that the second stage is larger in the diameter andconcentrically inserted outside the first one. Namely, the second stagebed 146 consists of a bed of the granules placed between cylindricallouvers 148, the upper part of the outer louver being connected to aninlet nozzle 160 through a cone 161, and the lower part thereof beingconnected to a sleeve 163 through a cone 162. The sleeve 163 is looselycontacted with a lower opening part of the body 134 with a certainallowance, and a nozzle 164 is fixed to this lower opening part througha sleeve 165. In addition, a guide plate 166 is provided so that thegranules may be easily discharged from the nozzle 164. Further, for thegas seal of the space part 147 between the beds 145 and 146,partitioning plates 168 are provided at the upper and lower parts of thespace part, respectively, and also for the gas seal of the outer sidespace 149, a partitioning plate 170 is provided. In addition, the upperpart of the outer side space 149 constitutes a gas passage 151 asmentioned above. Since the thickness of the beds makes the resistance tothe gas flow, a higher resistance to the gas flow than those broughtabout by the thickness of the beds is provided at any other openingparts, whereby there is no fear of the short-circuit of the gas, e.g. agas leak from the bed 145 to the exit nozzle 159, a gas leak from thebed 146 to the nozzle 164, etc.

All of the above-mentioned structures constructed inside the body of thevessel 134 are fixed to the upper end-plate 135. Namely, the structuresinside the body 134 are constructed in suspended manner, and inside thelower end-plate 136, the nozzle sleeves 158 and 157 are slidablyconnected with each other and the sleeves 165 and 163 are also slidablyconnected, whereby it is possible to absorb the thermal expansion.

The granules to constitute the second stage bed are fed through a nozzle160, descend inside a cone 161 and form a moving bed in a space placedbetween the louvers 148; and further fulfill a ring-form space formedbetween the sleeves 157 and 163 and are withdrawn through the nozzle164. On the other hand, the gas passes through the beds so as to crossthem radially from the central part of the gas chamber 142 as shown byarrow marks in the lateral direction, and the dust, etc. contained inthe gas is caught by the bed granules.

As the granules of the first stage bed 145 and the second stage bed 146,spheres of calcined alumina, etc. having a diameter of 1 to 2 mm may bepreferably employed, and the granules of the first stage bed 172(indicated by X marks) and those of the second stage bed 174 (indicatedby O marks) may have either the same specification or different ones.The same specification may be convenient in the point of regeneration ofgranules after withdrawal from the vessel. In order to elevate theefficiency of dust removal in the second stage bed 146, for example thediameter of the granules 174 may be made somewhat smaller.

According to the above-mentioned granular bed filter, wherein aplurality of stages of granular beds are formed inside the pressurevessel, it is possible to elevate the efficiency of dust removal and atthe same time make the apparatus smaller or compact. Further, since theinside structures are constructed in a suspended manner and also thethermal sleeves are employed, the thermal expansion of the apparatus canbe absorbed easily, and the thermal deformation of the apparatus as wellas the short-circuit of the gas can be prevented.

Coal gas to be introduced into the granular bed filter 60 has atemperature of 400° to 500° C. and a pressure of 20 to 30 kg/cm² G, andif the regeneration furnace 22 connected to this granular bed filter 60is also under such a high pressure, the amount of combustion air i.e.fluidization air increases proportionally by an amount corresponding tothe pressure. As a result, the amount of auxiliary fuel also increases.Further, the combustion exhaust gas will be also under pressure,resulting in the necessity of recovering power by e.g. an expansionturbine, which makes the apparatus complicated. Thus, from thestandpoint of the economy of the system, it is preferable to operate theregeneration furnace 22 under normal pressures.

FIG. 8 shows a systematic view of an apparatus for operating theregeneration furnace 22 connected to the granular bed filter 60 undernormal pressures. On the pipeline connecting the granular bed filter 60to the regeneration furnace 22 are successively provided a rotary valve180, a lock valve 181, a lock hopper 182, a lock valve 183, a hopper 184and a rotary valve 185. Further, on the pipeline for recirculating thegranules regenerated in the regeneration furnace 22 to the granular bedfilter 60, are successively provided a granule-blowing-up means 96, aprimary hopper 100, a secondary hopper 186, a lock valve 187, a lockhopper 188, a rotary valve 189, and a lock valve 190.

In order to operate the regeneration furnace 22 as a fluidized bedcombustion furnace under normal pressures (approximately the atmosphericpressure), the pressure of the granule atmosphere is reduced stepwiselydown to a normal pressure through the hoppers 182 and 184 and the lockvalves 181 and 183. Namely, the lock valve 183 is first closed and therotary valve 180 and the lock valve 181 are opened to feed a definiteamount of the granules into the lock hopper 182 under a lower pressure,followed by closing the lock valve 181. The lock valve 183 is thenopened and the granules are received in the hopper 184 under a furtherlower pressure, followed by closing the lock valve 183. Further, therotary valve 185 is opened to introduce the granules into theregeneration furnace 22 under a normal pressure.

Next, the medium granules are cooled down to a temperature approximateto the operation temperature of the granular bed in the regenerationfurnace 22 and then sent by means of compressed air 99 through theblowing-up means 96 and the pipeline 98 to the upper hopper 100. Then,the hopper 186, lock valve 187, lock hopper 188, rotary valve 189 andlock valve 190 are successively opened or closed to elevate the pressureof the atmosphere of the granules, followed by feeding the granules tothe granular bed filter 60. By operating the regeneration furnace undernormal pressures, a small amount of the air 92 fed to the regenerationfurnace may be sufficient.

FIG. 9 shows a preferred embodiment of the regeneration furnace 22. Thisfurnace consists of two stage fluidized beds of an upper stage fluidizedbed 91A and a lower stage fluidized bed 91B connected to the bed 91Athrough an overflow pipe 198. Tar, etc. adhering to the granules areburnt in the upper stage fluidized bed 91A, and air to be used forcombustion in the upper stage fluidized bed 91A is preheated in thelower stage fluidized bed 91B and at the same time the regeneratedgranules are cooled therein. The granules in a hopper 184 are fedthrough a rotary valve 185 and a feed pipe 193 to the upper stagefluidized bed 91A. Air preheated in the lower stage fluidized bed 91B issent through a perforated plate 194 into the upper fluidized bed 91A,wherein tar, etc. adhering to the granules are burnt to regenerate thegranules. If the amount of heat is insufficient, an auxiliary fuel 128is fed, while if it is in excess, the excess amount of heat can berecovered by means of a heat transfer coil 93 provided in the fluidizedbed 91A. The resulting combustion waste gas is subjected to cooling andheat recovery by means of a waste heat recovery coil 95 provided insidean empty column part 195; sent through a duct 97 to a dust-collector 196where dust is finally caught; and exhausted through a pipeline 197 as aclean gas. The granules subjected to combustion treatment in the upperfluidized bed 91A descend through the overflow pipe 198 provided insidethe upper stage fluidized bed, to the lower stage fluidized bed 91Bwhere the granules are cooled by contacting directly with the combustionair 92, and on the other hand, the combustion air is heated. The cooledgranules are transported through the duct 94 to the top of the granularbed by means of the blowing-up means 96. The temperature of the mediumof granules leaving the fluidized bed 91B is preferably made similar tothat of the granular bed to maintain heat balance between them, which iseasily designed by selecting the height of the lower stage fluidized bedand the superficial velocity in the column.

According to the above-mentioned embodiment, it is possible toregenerate the granules contained in the granular bed filter 60 undernormal pressures; hence it is possible to reduce the respective amountsof combustion air and auxiliary fuel down to smaller ones than thoseunder high pressures, and also simplify the structure of the apparatus.

FIG. 10 illustrates an embodiment of the gas cooler 62 and the scrubber64 in the flow diagram shown in FIG. 5.

In FIG. 10, gas coolers 62A and 62B each have a plurality of heattransfer tubes 200 vertically arranged in a vertical type vessel and thelower ends of these heat transfer tubes 200 are opened inside respectivescrubbers 64A and 64B. Further the respective coolers 62A and 62B areconnected to a drum 109 through risers 111A and 111B and downcomers 112Aand 112B, and also function as a waste heat boiler. The drum 109 isprovided with a water feed line 114 and a steam discharge line 115. Ifonly one cooler of large capacity is employed, gas distribution to theheat transfer tubes 200 becomes uneven and hence the descendingcondition of steam inside the heat transfer tubes 200 is unbalanced. Forthis reason, and for making its open sweeping easier, a plurality ofcoolers of small capacity are employed. Although two coolers 62A and 62Bare shown in the figure, in the case of an amount to be treated, of 1000t/day, e.g. 6 coolers may be employed. On the other hand, the respectivescrubbers 64A and 64B provided just below the coolers 62A and 62B havetherein a nozzle 201 for spraying recovered tar sent through a line 127,and by spraying recovered tar through the nozzle 201 and contacting therecovered tar directly with the gas, gas cooling and recovery of tarmist are at the same time effected.

Coal gas cooled in advance down to 400° to 500° C. is passed through aline 88, then branched, passed through lines 88A and 88B and introducedinto gas coolers 62A and 62B. In the respective gas coolers, in order toprevent adhesion and solidification of tar onto the wall of the heattransfer tubes 200 and also to prevent uneven heat transfer of thetubes, the wall temperature of the heat transfer tubes is maintained atabout 200° C. or higher. Thus, there may be selected such a saturationtemperature of the discharge steam, e.g. 15 kg/cm² G in terms of thesteam pressure on the line 115 from the drum 109, that the gastemperature after cooling (the exit temperature of the heat transfertubes 200) and the wall temperature of the heat transfer tubes 200 canbe maintained e.g. at 250° C. and 200° C. or higher, respectively.Accordingly, the temperature inside the tubes is not reduced to 200° C.or lower, and the total surface of the heat transfer tubes is maintainedat a uniform temperature. The exit gas of the heat transfer tubescontains tar mist, which is removed by contacting it with recovered tarhaving a temperature of about 150° C. in the scrubbers 64A and 64Bdirectly following the heat transfer tubes. The above-mentionedtemperature (150° C.) of recovered tar sprayed inside the scrubbers hasbeen selected taking into consideration the fluidity and pumping of thetar inside the tubes. If the fluidity of tar is not hindered,temperatures lower than 150° C. may be employed. Thus, the tar and gasinside the scrubbers 64A and 64B are cooled down to about 200° C.; inthe state of a gas-liquid mixed phase, passed through ducts 108A and108B connected to the lower end nozzles 202A and 202B; and introducedinto a gas-liquid separator 116 where they are separated from eachother. This separator 116 is preferred to be of a cyclone type. It ispossible to simplify the apparatus by providing one separator per twocoolers as shown in the figure. Purified gas obtained by separating tarmist is exhausted through a duct 118 to the outside of the system. Onthe other hand, recovered tar is collected through a piping 120 into apot 122 and transported through a duct 124 and a pump 125 to a lowpressure boiler 126. Excess tar is discharged through a duct 128 to theoutside of the system and most part of the remainder is cooled down toe.g. 150° C. in the low pressure boiler 126 and then delivered through aduct 127 to a scrubber nozzle 201. As to the low pressure boiler 126, itis necessary to maintain the wall temperature of the heat transfer tubesat a temperature of 150° C. or higher at which the tar fluidity is kept,as in the case of the coolers; hence it is preferable to make thepressure inside the tubes a saturated vapor pressure corresponding tothe above temperature. As a concrete example, the boiler 126 is sodesigned as to give 3 kg/cm² G as the pressure of generated steam 204(saturation temperature: about 140° C.) and 150° C. or higher as the tartemperature inside the heat transfer tubes in the boiler 126, while thetemperature of feed water 203 is normal.

According to the above-mentioned embodiment when the gas containing mistof adherent substances such as tar is cooled, it is possible to preventadhesion and solidification of these adherent substances and effectwaste heat recovery such as heat-exchange type recovery through steamformation; hence the thermal economy of plant is improved. Further, byemploying recovered tar for the scruffers, cooling, dust removal and tarremoval become easier without introducing any cooling medium from theoutside of the system; hence it is possible to effectively utilize thetar which causes obstacles to the utilities of plant.

What is claimed is:
 1. A process for the recovery of heat in coalgasification which comprises:(a) generating gas in a coal gasificationfurnace; (b) introducing the gas into a granular bed means provided withheat transfer tubes having cooling medium passing therethrough therebycooling the gas; (c) recovering the heat of the gas in the granular bedmeans as heated cooling medium; (d) passing the gas cooled in (b)successively through a gas cooler and a scrubber, to cool the gas andremove dust and tar mist therefrom; andrecovering the heat of the gascooled in step (d), wherein said granular bed means includes a fluidizedbed cooler, in which said heat transfer tubes are located, and agranular moving bed filter, said gas being introduced into the fluidizedbed cooler and unnecessary substances including tars which are in thegas are adhered to the granules in the fluidized bed cooler and then thegas is introduced into the granular bed filter where dust in the gas isremoved by adherence to the granules in the filter, and wherein thecooling medium is water, the heat of the generated gas is recovered inthe form of high pressure steam through the heat transfer tubes in thegranular bed means, the heat in the gas cooler and the scrubber isrecovered in the forms of medium pressure steam and of low pressuresteam respectively.
 2. A heat recovery process according to claim 1wherein said granular bed filter comprises a body consisting of avertical type vessel; a gas-introducing passage provided at the axiallycentral part of said body; a plurality of louver-form walls provided soas to concentrically surround said gas-introducing passage withring-form spaces; a means for forming moving beds by feeding granulesinto the respective ring-form spaces between these louver-form walls;and nozzles for discharging the gas having passed through saidlouver-form walls and said moving beds of granules to the outside ofsaid body, the respective upper ends of said louver-form walls beingfixed onto said body through a granule-feeding duct, the respectivelower ends of said walls being connected to a granule-discharging duct,and the respective granule-discharging ducts being slidably contactedwith the opening part of said body at the lower end part thereof so asto enable these granule-discharging ducts to effect easy thermalexpansion.
 3. A process according to claim 1 wherein granules havingunnecessary substances adhered thereto and granules having dust adheredthereto are withdrawn from the fluidized bed cooler and the granular bedfilter, respectively, are regenerated in a fluidized bed combustionfurnace by subjecting the granules to a combustion treatment therein andare recirculated to the fluidized bed cooler and to the granular bedfilter.
 4. A heat recovery process according to claim 3 wherein saidfluidized bed-combustion furnace is provided with an upper stagefluidized bed and a lower stage fluidized bed, said lower stagefluidized bed being connected to said upper stage bed through anoverflow pipe; in said upper stage fluidized bed, unnecessary substancesadhering to the granules are burnt; and in said lower stage fluidizedbed, air to be fed to said upper stage fluidized bed is preheated and atthe same time the regenerated granules flowing down through saidoverflow pipe are cooled.
 5. A heat recovery process according to claim3 wherein the regeneration furnace is operated under normal pressure. 6.A heat recovery process according to claim 5 wherein the regenerationfurnace is provided with a lock valve and a lock hopper in each of agranules feed pipe and a granules discharge duct, respectively, saidlock valve and lock hopper operating alternately.
 7. A heat recoveryprocess according to claim 1 wherein said gas cooler consists of avertical type vessel wherein a plurality of heat transfer tubes arevertically arranged and cooling water is passed through the vesseloutside of said heat transfer tubes, the lower ends of these heattransfer tubes being opened inside the scrubber containing nozzles forspraying recovered tar, and the gas cooled by passing through said heattransfer tubes being introduced directly into said scrubber andcontacted with recovered tar of lower temperature than the gasintroduced into said scrubber.
 8. A heat recovery process according toclaim 7 wherein said gas cooler is connected to a condensation drum by ariser and a downcomer, and the heat of the gas passing through said heattransfer tubes is recovered in the form of medium pressure steam throughsaid condensation drum.
 9. A heat recovery process according to claim 7wherein said scrubber is further connected to a gas-liquid separator tocondense and recover tar from the gas from said gas cooler and isprovided with a means for recirculating the recovered tar to saidscrubber and also is provided with a heat-exchange means for recoveringthe heat of the recovered tar in the form of low pressure steam.
 10. Aprocess according to claim 2 wherein a plurality of ring-form concentricmoving beds are provided in the granular bed filter, said moving bedsbeing separated by ring-form gas chambers having louver-form walls. 11.A process according to claim 10 including passing the gas radially fromthe introducing passage through the concentric moving beds separated bygas chambers toward the outer periphery of the vessel thereby removingdust from the gas and discharging the dust-free gas through nozzle meansin the outer periphery.
 12. The process according to claim 2 wherein themoving bed thickness is 500-600 mm.
 13. The process according to claim4, wherein the upper stage bed is provided with a heat transfer coilthereby recovering the excess heat of combustion produced in the upperstage bed.
 14. The process according to claim 7, wherein medium pressuresteam having a saturated temperature corresponding to 200° to 250° C. isproduced, wherein the temperature of the surface of the heat transfertubes is maintained above 200° C. and further wherein the gas is cooledto a temperature of approximately 250° C.
 15. The process according toclaim 7 wherein the temperature of the recovered tar is approximately150° C.